Abstract 15731: Hypoxia and Akt Induced Stem Cell Factor Exerts Cardioprotective Effects via Specific Binding to the Insulin-Like Growth Factor-1 Receptor
Introduction: Myocardial infarction results in the death of large numbers of cardiomyocytes which are not replaced. We have recently identified a protein, Hypoxia and Akt induced Stem cell Factor (HASF), which inhibits cardiomyocyte apoptosis and promotes the proliferation of these cells. Although the therapeutic effects of HASF were clearly demonstrated, critical aspects of the signaling pathway, namely the identity of the receptor, were unclear. Here, we report that HASF binds and signals through the Insulin-like Growth Factor-1 Receptor (IGF-1R).
Methods: Mouse cardiomyocytes were isolated by the Langendorff technique. Yeast two-hybrid and co-immunoprecipitation were used to identify HASF binding proteins. Kinase activation and GLUT4 translocation were assessed by immunoblot analysis.
Results: A yeast two-hybrid screen identified a partial fragment of the IGF-1R as a binding partner of HASF. Direct interaction between HASF and the full-length IGF-1R was subsequently identified via co-immunoprecipitation experiments using HEK293 cell lysates (N=3). Treatment of neonatal ventricular cardiomyocytes with either 100nM HASF or 100nM IGF-1 resulted in equivalent activation of IGF-1R (N=3) and IGF-1R regulated kinases (Akt, PKCe, PKCz, ERK. N=3). IGF-1R phosphorylation was significantly increased in mice over-expressing HASF (p<0.01). Equivalent concentrations of HASF and IGF-1 (100nM) induced the translocation of the glucose transporter GLUT4 to the plasma membrane of cardiomyocytes (N=3, p<0.05). HASF activation of Akt, PKCe and PKCz was completely abrogated by the IGF-1R specific inhibitor picropodophyllin (N=3, p<0.01). Similarly knockdown of IGF-1R by siRNA blocked HASF from activating the kinases Akt, PKCe and PKCz (N=3, p<0.01). In contrast, knockdown of IGF-2R had no effect on HASF signaling (N=3, p<0.01).
Conclusion: Our studies have identified IGF-1R as the HASF receptor. The implication that HASF and IGF1 share functional similarities is important information for the therapeutic uses of both proteins.
Author Disclosures: A. Bareja: None. C. Hodgkinson: None. A. Payne: None. R. Pratt: None. V. Dzau: None.
This research has received full or partial funding support from the American Heart Association.
- © 2014 by American Heart Association, Inc.